In many commercial processes and manufactured materials (e.g., catalysis, coating compositions, lubricants, medical treatment and cosmetic manufacture) it is desirable to use solid particles to carry liquids or to treat the surface of particles with liquids. Liquids have been traditionally applied by batch mixing of liquids and particles in a drum, and some amount of drying is also associated with such processes to reduce the total liquid content from that necessary to assure coating of all surfaces down to that amount actually necessary or desired on the coated particles. This methodology of liquid application is quite crude, does not provide assurance of equal coating quality on the particles, allows for or even causes significant agglomeration of particles, and, when drying is involved, requires liquid/solvent recovery techniques which tend to be expensive. Additionally, the conventional liquid coating and treatment process for particles alters the particle size distribution of the particles, either damaging the particles (and lowering average particle size) or causing particle agglomeration (which gives an apparent increase in average particle size).
Fluidized beds are systems in which volumes of solid particulates (called `beds`) are transformed into a fluid-like state by the forced passage of gas upwardly through the bed of particles. Once a sufficient velocity and volume of gas passes upward through the particle bed, the drag forces of the moving gas (with a positive vertical vector) at least equals the gravitational force (a negative vertical vector) on the individual particles. The particles then become supported in gas flow, giving the appearance of a liquid mass, being capable of adjusting to dimensional changes and the like. The mass of particles supported in a condition which mimics conventional fluids by the upward flow of gas is known as a fluidized bed. Fluidized beds or their equivalents are known to be generated by electrostatic fields on particles (e.g., electrostatic fluidized beds as have been described for use in electrostatic coating operations) and by magnetic fields applied to magnetic particles (e.g., U.S. Pat. No. 3,848,363, Lovness). U.S. patent application Ser. No. 08/518,640, filed on Aug. 25, 1995, also describes the use of this type of magnetic fluidization system to apply conventional fluidization size (100 microns or greater) solid particulates to other surfaces by fluidizing the magnetic particles and having them impact surfaces introduced into the magnetically fluidized bed, the impact of the fluidized solid particles embedding or otherwise adhering the fluidized particles to the introduced surfaces. That Application describes the coating of only solid surfaces with solid coating materials (with coating materials such as aluminum oxide particles and phenolic powder applied to non-woven thermoplastic scouring material to increase the abrasiveness; magnetic coatings such as iron oxide can be applied to polymeric substrates such as polyester films to provide magnetic recording media; and with high cost coating materials applied to low cost substrates to achieve desired properties with cost benefits. For example, pigments and reflective materials can be coated onto hollow glass spheres to provide desired optical qualities. Fragile reactive coatings such as chelating agents, e.g., algae, can be applied to substrates to achieve desired reactive materials. Precious metals such as gold, silver or platinum can be applied to substrates to achieve desired aesthetic effects.